Haoyuan Cai

Fabrication and characterization of microelectromechanical systems-based gas chromatography column with embedded micro-posts for separation of environmental carcinogens

In this paper, a micro gas chromatography (μGC) column with embedded micro-posts was developed for increasing overall surface area of the columns which is able to support more of the stationary phase and reducing the effective width of the column, leading to higher separation efficiency. The proposed columns have a higher sample capacity as the overall surface area is about 3 times larger than that of open columns with the same dimensions. In order to achieve an even flow velocity in the channels, the location of the micro-posts in the linear channels and the configuration of curved channels were optimized by numerical simulation. The results have indicated that the proposed column separated 5 environmental carcinogens in less than 50s, achieved a separation efficiency of about 9500plates/m and eluted highly symmetrical Gaussian peaks.

Microfluidic Biochip for Blood Cell Lysis

Abstract Based on the micro-electro-mechanical system (MEMS) technology, a sandwich flow microfluidic biochip for blood cell lysis was designed and fabricated. The cell solution was sandwiched in between the chemical reagent solution, and both were introduced into the biochip. The two solutions were then flowing through the microchannel of the biochip. Finally, cells lysis was brought about by complete blend of the cell solution and the chemical reagent solution during continuous flow. Rat blood with anticoagulant was the cell sample, while guanidine and Triton X-100 were used as the lysing reagents, respectively, and the effects of the two reagents on cell lysis were compared. The effects of the cell concentration and the flow rate on cell lysis were analyzed using guanidine as the lysing reagent. Blood cells can be lysed in a few minutes when the flow rate of the lysing reagent is considerably faster than the flow rate of the cell sample. Blood cells can be rapid lysed in microfluidic biochip when the flow rates of the lysing reagent and the cell sample are increased simultaneously in the above proportion. The sandwich-type microfluidic biochip for cell lysis potentially integrated with the biochip for cell separation and the biochip for DNA extraction could enable complete pretreatment of complex biologic samples, which can lay the foundation for the realization of the micro total analytic system (μ TAS).

Use of surface plasmon resonance to investigate lateral wall deposition kinetics and properties of polydopamine films

Dopamine (DA) is a particularly important neurotransmitter. Polydopamine (pDA) films have been demonstrated to be important materials for the immobilization of biomolecules onto almost any type of solid substrate. In this study, a surface plasmon resonance (SPR)-based sensor system with the sensor chip surface parallel to the direction of gravity was used to investigate the lateral wall deposition kinetics and properties of pDA films. The deposition kinetics of pDA Films are limited by the oxidation process. The pDA film could not be removed from the sensor chip completely by a strongly alkaline solution, indicating that the pDA film was heterogeneous in the direction of deposition. The pDA film formed near the interior of the solution was less stable than the film formed near the gold-solution interface. Adsorption of proteins on pDA film was studied compared with that on bare gold and dextran sensor chip. The reduction of Au(111) cations by the pDA film, forming a layer of gold particles, was monitored using SPR.

A micro gas chromatography column with a micro thermal conductivity detector for volatile organic compound analysis

In this paper, a micro gas chromatography (μGC) system contained a μGC column and a micro thermal conductivity detector (μTCD) was proposed. In order to reduce the volume of the system, some micro heaters were integrated on the surface and backside of the GC column, which could provide a robust temperature programming capability and rapidly increase the temperature of the μGC column. In addition, a silicon-glass μTCD with four-thermistor thermal conductivity cells that can offer significant advantages over previously reported designs including low dead volume, good thermal isolation, and elimination of the thermal noise was proposed in this paper. Experimental results have indicated that the μGC system with a detection limit of several ppm concentration levels separated and detected the benzene, toluene, and styrene in less than 3 min, and the μGC system also exhibited a good linear response in the test range.

Apparatus for measuring the Seebeck coefficients of highly resistive organic semiconducting materials

A Seebeck coefficient measurement apparatus for high resistance organic semiconductor materials has been designed and built. It can measure materials with resistance over 7 × 10(12) Ω. This is the highest material resistance value ever reported for Seebeck coefficient measurement. A cyclic temperature gradient generation technique and a corresponding algorithm are proposed to eliminate the negative effects of the long term drift of Seebeck voltage. Sources of errors in these measurements are discussed.

Fabrication of Solid Phase Extraction DNA Chips Based on Bio-Micro-electron-Mechanical System Technology

Abstract In this work, a novel solid phase extraction (SPE) deoxyribonucleic acid (DNA) microfluidic chip with silicon-PDMS-glass structure was fabricated based on bio-micro-electro-mechanical system (BioMEMS) technology. Four kinds of solid phase matrixes were fabricated on silicon substrates, and the characteristics of these matrixes were analyzed. The porous oxidized silicon was optimally selected as the solid phase matrix for purification DNA (deoxyribonucleic acid). The different sealing technologies were contrastively developed for sealing the chip to form a close channel. The polydimethylsiloxane-glass (PDMS-glass) cover was fabricated using the optimal pressing method and the silicon substrate with the solid phase matrix was bonded with the PDMS-glass cover to accomplish the preparation of the SPE chip. This SPE chip was used successfully for purification genomic DNA from the rat whole blood. DNA of 23.5ng was extracted from per microlitre whole blood and the extracted DNA was successfully amplified by PCR, which could reach the level of the commercial DNA purification kits. Furthermore, the SPE microfluidic chips have the potential to be integrated with other sample preparation microchips, PCR microchip, capillary electrophoresis microchip and so on to achieve detection and analysis of the complex biological samples.

Continuous Immunoassay for Sulfamethazine by Surface Plasmon Resonance-Based Biosensor

Regeneration of the sensor chip surface is difficult in many surface plasmon resonance (SPR) biosensor assays. Improper regeneration will reduce life span of the sensor chip and decrease the quality of the data. Considering the advantages of reducing the regeneration frequency, a theoretically feasible continuous SPR biosensor immunoassay for sulfamethazine (SMT) was developed. In the continuous inhibitive immunoassay, the sensor chip surface is regenerated only once after a definite number of tests instead of every test. The SMT-bovine serum albumin (BSA) conjugate was covalently immobilized to a carboxymethyldextran modified gold film. The immobilization conditions of the antigen were studied and the working dilution of the antibody was optimized. The antibody was mixed with SMT of different concentrations prepared with PBS buffer to construct the calibration curve. The limit of detection was 0.5 ng mL−1. The continuous SPR biosensor assay was proved to be simpler and more practical than a normal one.

Surface Plasmon Resonance characteristic study of graphene-on-gold structure

In this paper, we carried out an experimental study of graphene-on-gold structure based on Surface Plasmon Resonance Imaging (SPRI) method. To our knowledge, this is the first experimental report of graphene SPR study. An experimental SPRI platform was setup, which can fulfill wide incident angle range covering the resonant angle of gas and aqueous sample. 1, 2, 3 layers of graphene are fabricated by CVD method and then transfer to gold substrate. The SPR images of different graphene-on-gold structure are acquired and analyzed. SPR curves of different layers of graphene-on-gold are obtained and compared with simulation result. It is found that the SPR angle will shift about 0.18(deg) per graphene layer, which is consistent with the simulation result (0.15 deg). The graphene-on-gold structure provide an accurate single-atom-layer tool, which can be applied in various research areas, e.g. biosensor, nanoplasmonic etc.

Portable surface plasmon resonance instrument based on a monolithic scanner chip

A portable Surface Plasmon Resonance (SPR) instrument based on a monolithic scanner chip — LM9833 was developed. With this compact design, the instrument can provide 16 bit grayscale resolution at 100 frames per second, support up to 16384 pixels linear CCD sensor, enable illumination control and USB interface. The instrument performance was tested and the refractive index sensitivity is about 6×10−5 RIU (Refractive Index Unit). A direct immunoassay was carried out with this instrument and 15µg/ml Human Serum Albumin (HSA) could be detected.

A poly(dimethylsiloxane) based prism for surface plasmon resonance imaging system and its application for gas detection

This paper presents a surface plasmon resonance (SPR) imaging system based on a low-cost, convenient poly(dimethylsiloxane) (PDMS) prism featured with a close contact with the gold film. Compared to conventional glass prism, both numerical simulations and experimental studies indicated a deeper but wider absorption peak with a higher coupling angle for the PDMS based prism. System repeatability was quantified by the cycled detection of helium and air, with the effect of the flow rate investigated. Furthermore, five types of gases (nitrogen, air, oxygen, hydrogen, and helium) were detected and differentiated by the SPR system, with a calculated sensitivity of 5 × 10(-6) RIU.